MINISTRY OF AGRICULTURE, FISHERIES AND FOOD CSG 15 Research and Development Final Project Report (Not to be used for LINK projects) Two hard copies of this form should be returned to: Research Policy and International Division, Final Reports Unit MAFF, Area 6/01 1A Page Street, London SW1P 4PQ An electronic version should be e-mailed to [email protected] Project title Characterisation and pathogenesis of epizootics in wild freshwater fish (Phase II) MAFF project code FC1106 Contractor organisation and location CEFAS Weymouth Laboratory, Barrack Road, Weymouth, Dorset. DT4 8UB Total MAFF project costs £ Project start date 01/04/96 Project end date 31/03/00 Executive summary (maximum 2 sides A4) This contract provided information on a number of fish disease issues including the assessment of epizootics affecting wild fish populations and the possibility of introduction of exotic parasites via the importation of cold water ornamental fish. Epizootics amongst cyprinid fry caused by myxosporean parasites were investigated in liaison with the Environment Agency (EA). Several thousand fry, mainly roach (Rutilus rutilus), chub (Leuciscus cephalus), dace (Leuciscus leuciscus) and minnow (Phoxinus phoxinus) were collected and examined histologically for myxosporean infections. The main parasite of concern has been identified as Myxobolus cyprini, which primarily affects the muscle tissues. Chub appear to be most susceptible and based on the pathological response, fish with heavy infections are certainly debilitated and some are unlikely to survive. However, levels of infection fluctuate from year to year and between different rivers sampled in the same year. Chub fry from certain locations also exhibit skeletal deformities and these were found to be associated with another myxosporean parasite. Whether affected fish survive is at present uncertain although occasional adult fish exhibiting skeletal deformity do occur. In liaison with the CEFAS Fish Health Inspectorate (FHI) reports of severe eye pathology and blindness in sea trout and salmon during 1996 and 1997 were investigated. Histopathological findings indicated that the early stages involved degenerative changes to the cornea resulting in various degrees of opacity. However, most samples examined were of more advanced cases where the eyeball had ruptured. In these cases marked necrosis and and inflammation associated with secondary bacterial invaders made it impossible to determine the original cause of the lesion. There were very few reported cases in 1998/99. CSG 15 (Rev. 12/99) 1 Project Characterisation and pathogenesis of epizootics in wild MAFF FC1106 title freshwater fish (Phase II) project code Examinations for parasites found in imported cold-water ornamental fish were conducted. The aim was to identify parasites occurring in these fish in order to asses their pathogenicity and to determine whether suitable alternate hosts, necessary for completion of life cycles were already present within the UK. This information being essential to assess the potential threat to indiginous fish stocks. By far the most parasite species were detected in fish that were believed to have been collected from wild sources. In contrast, farm bred fish such as koi carp showed very few parasites species to be present. No parasite species known to be specific pathogens to native fish were detected and it was concluded that the actual risk of introduction and establishment of new species of fish parasites to the UK was relatively small. However, surveillance should continue in order to maintain awareness of potential parasite pathogens being introduced via imports of cold- water ornamental fish. Disease epizootics were investigated in liaison with the FHI and the EA. Bullheads from the River Allen exhibiting external cysts were examined histologically and were found to contain spores of a Dermocystidium species. Host reaction was usually mild , but in some cases an inflammatory response was present. The exact identity of the parasite and its relationship to the salmonid infecting species requires clarification. An epizootic affecting pond-reared carp was found to be caused by the myxosporean parasite Sphaerospora molnari. Severe gill pathology was noted associated with mortalities. This was believed to be the first record of this parasite in the UK. A survey of the parasite fauna of juvenile salmonids was undertaken with the FHI. Special attention was given to the prevalence of proliferative kidney disease (PKD) and other renal myxosporeans since this information from wild fish was almost totally lacking. Macroscopic signs of PKD were noted in brown trout with salmon also being affected by the disease in several rivers. Histological examination of tissues revealed the presence of the causative agent (Tetracapsula bryosalmonae) in most trout but fewer of the affected salmon. Many fish were found to be infected with another myxosporean parasite Chloromyxum sp. (possibly an undescribed species) but the host response to this species was generally minimal. A Sphaerospora sp. was also recorded. Whether these parasites affect the development or severity of PKD requires clarification. However, the sporogonic stages do not elicit a strong host reaction. For the full parasite survey a total of 215 trout, 160 salmon, 16 charr and 5 grayling were examined. Twenty- six parasite taxa were found in the four species of juvenile salmonids examined, comprising seven myxozoans, two protistans, four monogeneans, two digeneans, three cestodes, five nematodes and three acanthocephalans. Protista were only recorded in trout and salmon, trout having a more diverse myxozoan fauna. The ciliate Spironucleus barkhanus was found in the gall bladders of two brown trout in Cornwall. This being the first record of this parasite in the UK. This is a significant finding since it is known that this parasite can be highly pathogenic in salmon and other salmonids. However, pathogenicity in native brown trout is unknown. Discocotyle sagittata and Gyrodactylus derjavini were found in two samples of salmon. Crepidostomum farionis was present in all four species of fish and in most rivers. Cestodes were only found in the small sample of charr. Nematodes were present in trout, salmon and charr, with Cystidicoloides ephemeridarum found at high prevalences. Trout, salmon and charr were hosts for the acanthocephalan Echinorhynchus truttae; grayling were hosts for Acanthocephalus anguillae (a new host record), and Pomphorhynchus laevis. No copepods were found despite extensive searches. Examples the various lesions and parasite specimens encountered during this project were lodged in the Registry of Aquatic Pathology (RAP) collection housed at CEFAS Weymouth. The collection contains examples of pathological material from a wide range of fish and shellfish, mainly based on histological material and is used both for reference and training purposes. The scope of the collection was increased to incorporate parasite specimens, updated to a database format and all records were transferred to the new database. Representative images have been incorporated to be available alongside the other specimen information and it is planned that eventually, the RAP will be available as a CD ROM. CSG 15 (1/00) 2 Project Characterisation and pathogenesis of epizootics in wild MAFF FC1106 title freshwater fish (Phase II) project code Scientific report (maximum 20 sides A4) The main aim of this project was to provide authoritative scientific advice to MAFF on the significance and importance of parasites and diseases in native wild and farmed fish stocks. In particular to provide assessments of the significance of emergent disease problems in order to underpin policy decisions on preventing serious fish disease and parasitism in wild freshwater fish. Initially the project was conducted on an opportunistic basis responding in particular to investigation of specific disease outbreaks, often in conjunction with the Fish Health Inspectorate (FHI). However, student placements were used to provide additional resource and were instrumental in allowing more in depth studies to be undertaken on specific topics. Their contribution is indicated in the text and the full reference to their work is included in the list of outputs provided at the end of this report. The main scientific objectives of this project were as follows: - 1. Investigate and assess the threat of introduction of exotic pathogens via the importation of cold- water ornamental fish. 2. Investigate the occurrence of epizootics in wild freshwater fish populations and provide authoritative assessments of their significance. 3. Provide scientifically based information and advice to underpin policy decisions on preventing serious fish disease and parasitism in wild freshwater fish. During the lifetime of this project it was possible to address several issues concerning disease in wild fish populations and the work programme centred around four main themes. These themes were essentially independent of each other but provided scientific information on a wide variety of conditions either occurring in wild fish populations or of potential threats to native stocks. These themes will be dealt with separately in this report. A) Examination of cyprinid fry from a variety of river systems for significant parasitism and, in liaison with the Environment Agency (EA) investigate possible effects on recruitment. This work was initiated because of concerns about the possible decline in wild fish populations in